Reland "[heap] Fine-grained JSArrayBuffer tracking"

src/heap/array-buffer-tracker.h

Index: src/heap/array-buffer-tracker.h
diff --git a/src/heap/array-buffer-tracker.h b/src/heap/array-buffer-tracker.h
index 6130003d15263fff94d56070d44a4713858ab9da..e3f06bc8552eb887abcdd6fd620630cc62ece603 100644
--- a/src/heap/array-buffer-tracker.h
+++ b/src/heap/array-buffer-tracker.h
@@ -7,6 +7,7 @@
 
 #include <map>
 
+#include "src/allocation.h"
 #include "src/base/platform/mutex.h"
 #include "src/globals.h"
 
@@ -15,61 +16,110 @@ namespace internal {
 
 // Forward declarations.
 class Heap;
+class Page;
 class JSArrayBuffer;
 
-class ArrayBufferTracker {
+// LocalArrayBufferTracker is tracker for live and dead JSArrayBuffer objects.
+//
+// It consists of two sets, a live, and a not yet discovered set of buffers.
+// Upon registration (in the ArrayBufferTracker) the buffers are added to both
+// sets. When a buffer is encountered as live (or added is live) it is removed
+// from the not yet discovered set. Finally, after each round (sometime during
+// GC) the left over not yet discovered buffers are cleaned up. Upon starting
+// a new round the not yet discovered buffers are initialized from the live set.
+//
+// Caveats:
+// - Between cleaning up the buffers using |Free| we always need a |Reset| and
+//   thus another marking phase.
+// - LocalArrayBufferTracker is completely unlocked. Calls need to ensure
+//   exclusive access.
+class LocalArrayBufferTracker {
  public:
-  explicit ArrayBufferTracker(Heap* heap) : heap_(heap) {}
-  ~ArrayBufferTracker();
+  typedef std::pair<void*, size_t> Value;
+  typedef JSArrayBuffer* Key;
 
-  inline Heap* heap() { return heap_; }
+  enum LivenessIndicator {
+    kForwardingPointer,
+    kMarkBit,
+    kForwardingPointerOrMarkBit
+  };
+  enum CallbackResult { kKeepEntry, kKeepAndUpdateEntry, kRemoveEntry };
 
-  // The following methods are used to track raw C++ pointers to externally
-  // allocated memory used as backing store in live array buffers.
-
-  // A new ArrayBuffer was created with |data| as backing store.
-  void RegisterNew(JSArrayBuffer* buffer);
+  explicit LocalArrayBufferTracker(Heap* heap) : heap_(heap), started_(false) {}
+  ~LocalArrayBufferTracker();
 
-  // The backing store |data| is no longer owned by V8.
-  void Unregister(JSArrayBuffer* buffer);
+  void Add(Key key, const Value& value);
+  void AddLive(Key key, const Value& value);
+  Value Remove(Key key);
+  void MarkLive(Key key);
+  bool IsEmpty();
 
-  // A live ArrayBuffer was discovered during marking/scavenge.
-  void MarkLive(JSArrayBuffer* buffer);
+  // Resets the tracking set, i.e., not yet discovered buffers are initialized
+  // from the remaining live set of buffers.
+  void Reset();
 
-  // Frees all backing store pointers that weren't discovered in the previous
-  // marking or scavenge phase.
-  void FreeDead(bool from_scavenge);
+  // Frees up any dead backing stores of not yet discovered array buffers.
+  // Requires that the buffers have been properly marked using MarkLive.
+  void FreeDead();
 
-  // Prepare for a new scavenge phase. A new marking phase is implicitly
-  // prepared by finishing the previous one.
-  void PrepareDiscoveryInNewSpace();
+  // Scans the whole tracker and decides based on liveness_indicator whether
+  // a JSArrayBuffer is still considered live.
+  template <LivenessIndicator liveness_indicator>
+  inline void ScanAndFreeDead();
 
-  // An ArrayBuffer moved from new space to old space.
-  void Promote(JSArrayBuffer* buffer);
+  bool IsTracked(Key key) { return live_.find(key) != live_.end(); }
 
  private:
-  base::Mutex mutex_;
-  Heap* heap_;
+  // TODO(mlippautz): Switch to unordered_map once it is supported on all
+  // platforms.
+  typedef std::map<Key, Value> TrackingMap;
 
-  // |live_array_buffers_| maps externally allocated memory used as backing
-  // store for ArrayBuffers to the length of the respective memory blocks.
-  //
-  // At the beginning of mark/compact, |not_yet_discovered_array_buffers_| is
-  // a copy of |live_array_buffers_| and we remove pointers as we discover live
-  // ArrayBuffer objects during marking. At the end of mark/compact, the
-  // remaining memory blocks can be freed.
-  std::map<void*, size_t> live_array_buffers_;
-  std::map<void*, size_t> not_yet_discovered_array_buffers_;
-
-  // To be able to free memory held by ArrayBuffers during scavenge as well, we
-  // have a separate list of allocated memory held by ArrayBuffers in new space.
+  // Processes buffers one by one. The CallbackResult decides whether the buffer
+  // will be dropped or not.
   //
-  // Since mark/compact also evacuates the new space, all pointers in the
-  // |live_array_buffers_for_scavenge_| list are also in the
-  // |live_array_buffers_| list.
-  std::map<void*, size_t> live_array_buffers_for_scavenge_;
-  std::map<void*, size_t> not_yet_discovered_array_buffers_for_scavenge_;
+  // Callback should be of type:
+  //   CallbackResult fn(JSArrayBuffer*, JSArrayBuffer**);
+  template <typename Callback>
+  inline void Process(Callback callback);
+
+  Heap* heap_;
+
+  // |live_| maps tracked JSArrayBuffers to the internally allocated backing
+  // store and length. For each GC round |not_yet_discovered_| is initialized
+  // as a copy of |live_|. Upon finding a JSArrayBuffer during GC, the buffer
+  // is removed from |not_yet_discovered_|. At the end of a GC, we free up the
+  // remaining JSArrayBuffers in |not_yet_discovered_|.
+  TrackingMap live_;
+  TrackingMap not_yet_discovered_;
+
+  bool started_;
 };
+
+class ArrayBufferTracker : public AllStatic {
+ public:
+  // The following methods are used to track raw C++ pointers to externally
+  // allocated memory used as backing store in live array buffers.
+
+  // Register/unregister a new JSArrayBuffer |buffer| for tracking.
+  static void RegisterNew(Heap* heap, JSArrayBuffer* buffer);
+  static void Unregister(Heap* heap, JSArrayBuffer* buffer);
+
+  // Frees all backing store pointers for dead JSArrayBuffers in new space.
+  static void FreeDeadInNewSpace(Heap* heap);
+
+  static void FreeDead(Page* page);
+
+  template <LocalArrayBufferTracker::LivenessIndicator liveness_indicator>
+  static void ScanAndFreeDeadArrayBuffers(Page* page);
+
+  // A live JSArrayBuffer was discovered during marking.
+  static void MarkLive(Heap* heap, JSArrayBuffer* buffer);
+
+  // Resets all trackers in old space. Is required to be called from the main
+  // thread.
+  static void ResetTrackersInOldSpace(Heap* heap);
+};
+
 }  // namespace internal
 }  // namespace v8
 #endif  // V8_HEAP_ARRAY_BUFFER_TRACKER_H_